1. Field of the Invention
This invention relates broadly to a system and method for depositing diamond coatings on surfaces. More particularly, this invention relates to a system and method for coating a diamond film on a non-planar surface.
2. State of the Art
The utility of high quality diamond films for various applications is well known. Superior physical, chemical, and electrical properties make diamond films desirable for many mechanical, thermal, optical and electronic applications. For example, diamond has the highest room-temperature thermal conductivity of any material, a high electric field breakdown (xe2x88x92107V/cm), and an air stable negative electron affinity. These properties make possible high power, high frequency transistors and cold cathodes which cannot be made with any semiconductor other than diamond. In addition, the etch-resistance of diamond coatings, makes such coatings ideal for components of semiconductor etching devices.
One method for producing thin diamond coatings is by using a chemical vapor deposition (hereinafter xe2x80x98CVDxe2x80x99) system. In CVD systems, a mixture of hydrogen and a gaseous hydrocarbon, such as methane, is activated and contacted with a substrate to produce a diamond coating on the substrate. The hydrogen gas is disassociated into atomic hydrogen, which is then reacted with the hydrocarbon to form condensable carbon radicals. The carbon radicals are then deposited on a substrate to form a diamond film.
One manner of practicing CVD is with a plasma jet system. Referring to prior art FIG. 1, a plasma jet system 10 includes an engine 12 having a hydrogen gas inlet 14, a cathode 16, an engine wall 18, and an anode 20. The system 10 further includes a gas injection disc 22 having a plurality of injectors 24, a distribution head (nozzle) 26 which is directed toward a mandrel 28 on which a substrate 30 may be located, and a vacuum deposition chamber 32 surrounding the engine 12, the gas injection disc 22, the distribution head 26, and the mandrel 28. In operation, atomic hydrogen gas is introduced through the hydrogen gas inlet 14 and formed into a hydrogen plasma jet by means of a direct current arc, an alternating current arc, or microwave energy within the engine. The plasma torch is hot enough (typically approximately 10,000xc2x0K) to reduce gases to their elemental form. Hydrocarbon reagents are then introduced from the injectors 24 of the gas injection disc 22 into the plasma torch, and the torch is directed into the distribution head 26 such that a jet of the condensable reagents exits the distribution head and is directed toward the substrate 30 on the mandrel 28. The mandrel 28 is oriented normal to the distribution head 26 such that the jet is directed at the substrate 30 in a line-of-sight manner, and a diamond coating is created on the substrate.
For coating planar surfaces of objects larger than the jet and also for obtaining uniformity of coating and elimination of hot spots which may reduce the quality of the coating through the formation of temperature gradients, it may be advantageous to rotate the object beneath the distribution head, as described in U.S. Pat. No. 5,342,660 and as shown in FIG. 1.
However, when coating a non-planar surface, e.g., the inside surface of an object such as a ring or bowl, particularly where the inner diameter increases in a direction away from the jet, the line-of-sight nature of the jet makes it difficult to obtain a uniform coating or any coating at all in some areas. In addition, while rotation of an object is typically preferred for coating uniformity and minimization of temperature gradients, it may be impractical or impossible to rotate, within the confines of the chamber, objects which are relatively large, oblong, complex, and/or awkward (i.e., having an off-axis center of gravity). Moreover, even if it were possible to rotate or otherwise move large, oblong, complex, and/or awkward objects within the chamber, it may not be feasible or practical to do such at a speed which would minimize the temperature gradient to which the surface of the object would be subject.
For the foregoing reasons, there is needed a system and method for depositing diamond coatings on objects having non-planar surfaces, such that the coating is applied in a substantially uniform thickness while minimizing temperature gradients.
The present invention is a novel system and method for depositing a CVD diamond coating on a non-planar surface of an object. The system includes a deflector having a deflecting surface which resists diamond coating as well as a conventional plasma jet engine, injection disc, distribution head, and mandrel on which a substrate object may be provided. At least the exit of the distribution head and the mandrel are contained within a vacuum deposition chamber.
According to several embodiments of the invention particularly suited for coating inner diameter surfaces of objects, the deflecting surface of the deflector resists diamond coating by diamond forming reactive reagents produced by the system and is adapted to withstand the relatively high deposition temperatures. The deflector is positioned substantially axially relative to an axis of the distribution head, and thereby relative to the axis of the jet exiting the distribution head. The deflector is preferably generally wedge-shaped or conical and coupled to a motor which is adapted to rotate the deflector at a relatively high speed. The mandrel may be positioned partially or completely around the deflector. The deflector is oriented with respect to the distribution head and the mandrel such that a jet exiting the distribution head is deflected by the deflector onto a surface of the object positioned on the mandrel. The object surface may be non-planar.
According to another embodiment of the invention particularly adapted for coating the outer diameter surface of a ring-shaped object or a perimeter portion of a non-circular object, a rotatable mandrel is adapted to rotate an object non-axially relative to the jet from the distribution head. A preferably stationary deflector is situated beneath the distribution head and oriented to deflect the jet from the distribution head toward the non-planar surface object. When the object is rotated on the mandrel, its outer diameter or perimeter portion is coated with a diamond coating by the jet.
The several embodiments of the invention provide systems adapted to coat diamond films on non-planar surfaces. Additional advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures.